Cam mechanism for stencil duplicating machine

ABSTRACT

A reliable, small and light stencil duplicating machine comprises a printing section, a sheet feeding section, and a sheet discharging section. The printing section includes a printing drum for wrapping a stencil thereon, a press roller and parts associated with a printing process. The sheet feeding section feeds each printing sheet into a space between the printing drum and the press roller. A printed sheet is stripped off from the printing drum by a sheet separating member of the sheet discharging section, and is discharged onto a tray.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a stencil duplicating machine, and moreparticularly to stencil duplicating machine which includes a mechanismfor contacting and detaching a press roller with and from a printingdrum, and a mechanism for actuating a sheet separating pawl to separatea printed sheet from the printing drum.

2. Description of the Related Art

There is a conventional stencil duplicating machine which uses amechanism for contacting and detaching a press roller with and from aprinting drum without interfering with a stencil clamp (called "clamp"hereinafter) mounted on the printing drum. Such a mechanism includes apair of cams which are fitted on a shaft separate from a shaft for theprinting drum, and actuates the press roller in synchronization with theprinting drum.

Japanese Utility Model Laid-Open Publication No. Sho 59-59361exemplifies an improved mechanism for contacting and detaching a pressroller with and from a printing drum. Specifically, the mechanism isintegral with the printing drum and includes a pair of cam discs for thepress roller which are coaxially attached to the printing drum. Thephase of these cam discs is determined in such a manner that the pressroller is in contact with the printing drum while the press roller is incontact with base circles of these cam discs via a pair of rollers ascam followers, and that the press roller is out of contact from theprinting drum while it is in contact with large diameter portions of thecam discs via these rollers. During the contact with the base circles ofthe cam discs, the press roller is not interfered with the clamp.

Japanese Patent Laid-Open Publication No. Sho 61-262,125, for example,discloses a mechanism for preventing a sheet separating pawl from beinginterfered with a clamp in a stencil duplicating machine. During anon-sheet separating process, this mechanism allows the sheet separatingpawl to stay at a position centrifugally away from the surface of aprinting drum without interfering with the clamp. Such a position iscalled "second non-sheet separating position" (a first non-sheetseparating position will be described later).

In this mechanism, a cam which is disposed on one side of the printingdrum and also serves as a flange comes into contact with a cam followerwhich is disposed at one end of an arm for actuating the sheetseparating pawl, thereby operating the sheet separating pawl. Further,the mechanism includes a lever, which is used to adjust a space betweenthe surface of the printing drum and a tip of the sheet separating pawl,and is coaxial with the sheet separating pawl. This mechanism enablesthe sheet separating pawl to strip a printed sheet from the surface ofthe printing drum without contacting therewith even when the printingdrum is not completely circular or even when the printing drum vibrates.In other words, at the sheet separating position, the sheet separatingpawl always maintains a predetermined Space between the printing drumand itself.

Further, there have been proposed various methods of actuating the sheetseparating pawl, e.g. a method of actuating the sheet separating pawl byusing a cam which is mounted on a shaft independent of the shaft of theprinting drum but is operated in synchronization with the printing drum,or a method in which an arm for the sheet separating pawl is actuated ata proper timing.

In the first mentioned mechanism, the press roller is prone to a problemthat it does not always contact with the printing drum with a uniformpressure. In the second mentioned mechanism, little consideration istaken to units for pushing and supporting the press roller.

As for the sheet separating pawl actuating mechanism, the firstmentioned mechanism is prone to the following problems should it beapplied to a small stencil duplicating machine including a slenderprinting drum only for A4 size sheets. The stencil duplicating machineincludes a strip of screen leather adjacent to a clamp on the surface ofthe printing drum. The screen leather reinforces the trailing edge of amesh screen of the printing drum, projects approximately 1 to 2millimeters from the printing drum, and is approximately 40 to 50millimeters wide. Therefore, it is necessary to determine the size andcontact timing of cams for the sheet separating pawl so as to keep thesheet separating pawl at a position where it is not in contact with thescreen leather. This position is called "first non-sheet separatingposition". In the mechanism, the cams and cam followers are required tobe in contact with one another over a relatively large area of theprinting drum during the rotation of the printing drum. The sheetseparating pawl has to quickly return to the sheet separating positionvia the first and second non-sheet separating positions in succession. Atiming to set the sheet separating pawl at the first non-sheetseparating position can be easily determined. Conversely, a timing tolet the pawl return to the sheet separating position from the secondnon-sheet separating position is rather difficult since the tip of theseparating pawl might collide with the clamp while the sheet separatingpawl returns to the sheet separating position. The second timing cannotbe set unless the cams are enlarged.

The second mentioned sheet separating mechanism inevitably becomes largesince it has a complicated structure to operate the printing drum andassociated cam shafts in a synchronized manner. Such a complicatedstructure requires deliberate and time-consuming adjustment, and wouldlead to a reduced performance of the stencil duplicating machine.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a reliable, smalland light stencil duplicating machine, which includes a relatively smallprinting drum, enables a press roller to be in contact with the printingdrum with a uniform pressure. In the stencil duplicating machine, asimplified sheet separating mechanism precisely sets timings to assure aquick return of a sheet separating pawl to the sheet separating positionvia first and second non-sheet separating positions.

In a first embodiment of the invention, there is provided a stencilduplicating machine comprising: a printing drum for wrapping a stencilthereon; a press roller selectively movable between a printing positionin pressure contact with the printing drum via a printing sheet and anon-printing position away from the printing drum; a press roller armfor rotatably supporting opposite ends of the press roller, the pressroller arm performing a rocking motion; at least one cam substantiallyintegral with a side of the printing drum, the cam being coaxiallysupported on a center shaft of the printing drum, having a largediameter portion at a part thereof, and selectively displacing the pressroller at the printing position and non-printing position; at least onepress roller cam follower fitted on a press roller shaft, the pressroller cam follower following the cam; a sheet separating member forstripping a printed sheet off from the surface of the printing drum; anda member for urging the press roller cam follower toward the cam.

According to a further aspect of the invention, there is provided astencil duplicating machine comprising: a printing drum for wrapping astencil thereon; a press roller selectively movable between a printingposition in pressure contact with the printing drum via a printing sheetand a non-printing position away from the printing drum; a press rollerarm for rotatably supporting opposite ends of the press roller, thepress roller arm performing a rocking motion; a sheet separating pawlselectively movable between a sheet separating position to strip aprinted sheet from the outer surface of the printing drum and anon-sheet separating position away from the printing drum; a shaft forfixedly supporting a base of the sheet separating pawl and moving thesheet separating pawl between the sheet separating position and thenon-sheet separating position; an arm for selectively displacing thesheet separating pawl at the sheet separating position and the non-sheetseparating position, the arm being fitted on the shaft for the sheetseparating pawl; at least one cam substantially integral with a side ofthe printing drum, the cam being coaxially supported on a center shaftof the printing drum, having a large diameter portion at a part thereof,and selectively displacing the press roller at the printing position andnon-printing position; at least one press roller cam follower followingthe cam, the cam follower being fitted on a press roller shaft; a memberfor urging the press roller cam follower toward the cam; a cam followerfor the sheet separating pawl, the cam follower being fitted on thesheet separating pawl arm and following the cam; and a member for urgingthe sheet separating pawl cam follower toward the cam.

BRIEF DESCRIPTION OF THE DRAWINGS

In all Figures, identical parts have identical reference numbers.

FIG. 1 is a schematic view showing the configuration of a stencilduplicating machine to which the present invention is applicable.

FIG. 2 is a perspective view of a mechanism for contacting and detachingthe press roller with and from the printing drum and parts associatedtherewith, according to a first embodiment of the invention.

FIG. 3 is a side cross sectional view of the mechanism of FIG. 2 duringa printing operation.

FIG. 4 is a perspective view showing one of cams used in the mechanismof FIG. 2.

FIG. 5 is a side view showing the mechanism of FIG. 2 during theprinting and non-printing operations.

FIG. 6(a) and FIG. 6(b) are side views showing the configuration andoperation of one of press roller bearing holders.

FIG. 7 is a view similar to FIG. 2, but showing a mechanism foractuating a sheet separating pawl and other parts associated therewithin a second embodiment of the invention.

FIG. 8 is a side view showing the state in which a tip of the sheetseparating pawl is away from a screen leather on the printing drum.

FIG. 9 is a view similar to FIG. 8, but showing the state in which thetip of the sheet separating pawl is away from a clamp

FIG. 10 is a view similar to FIG. 8, but showing the state in which thetip of the sheet separating pawl is further away from the clamp.

FIG. 11 is a view similar to FIG. 8, but showing the state in which thetip of the sheet separating pawl is going to return to the sheetseparating position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The configuration and operation of the stencil duplicating machine willbe described with reference to preferred embodiments shown in thedrawing figures.

The main part of the stencil duplicating machine is disposed at a centerof a housing (not shown). Referring to FIG. 1, the stencil duplicatingmachine comprises a printing section 10, a sheet feeding section 20, anda sheet discharging section 30. The printing section 10 mainly includesa cylindrical printing drum 1 which carries a stencil 3 wrapped on theouter surface thereof. The sheet feeding section 20 is disposed at aleft position under the printing drum 1 so as to feed printing sheets Pto the printing drum 1. The sheet discharging section 30 is locatedopposite to the sheet feeding section 20 and discharges printed sheetsPa onto a tray 16.

As shown in FIG. 1, the printing section 10 includes a clamp 4, an inksupply 8, and a press roller 9 as well as the printing drum 1. Theprinting drum 1 is rotatable counterclockwise (as shown by the arrow)round a center shaft 2 by a motor (not shown). The clamp 4 functions tohold a leading edge of a stencil 3, is located across a part of thesurface of the printing drum 1, and is opened and closed. The ink supply8 is located in the printing drum 1, and includes an ink supply roller 5for supplying ink to the inner surface of the printing drum 1, a doctorroller 6 which is juxtaposed with a fine space against the ink roller 6,and an ink supply tube 2 (i.e. center shaft 2). The ink roller 5 and thedoctor roller 6 form an ink pool 7 therebetween when ink is suppliedthereto via the ink tube 2. The press roller 9 is located below the inksupply roller 5 via the printing drum 1. The press roller 9 isselectively movable between a printing position, where it comes intocontact with the printing drum 1 via the printing sheet P, and anon-printing position away from the printing drum 1. At the printposition, the press roller 9 is in contact with the printing area b ofthe printing drum 1 via the printing sheet P as shown in FIG. 3. At thenon-printing position, the press roller 9 stays away from thenon-printing area a of the printing drum 1, and does not interfere withthe clamp 4.

The sheet feeding section 20 includes a sheet feed tray 11 bearing astack of printing sheets P, a sheet feed roller 12, a pair of sheetseparating rollers 13a and 13b, and a pair of sheet conveying rollers14a and 14b. The sheet separating roller pair 13a and 13b separate eachprinting sheet P from the sheet stack. The sheet conveying roller pair14a and 14b convey each printing sheet P at a preset timing into a spacebetween the outer surface of the printing drum 1 and the press roller 9.

The sheet discharging section 30 comprises a sheet separating pawl 15for stripping a printed sheet Pa off from the outer surface of theprinting drum 1, a sheet separating mechanism 21, and a tray 16 forreceiving printed sheets Pa. The sheet separating mechanism 21 includesan endless conveyor belt 19 extending over a pair of rollers 17 and 18so as to convey the stripped sheet Pa onto the tray 16.

A stencil duplicating machine according to a first embodiment of theinvention will be described hereinafter with reference to FIGS. 2 to 6.

Referring to FIG. 2, the printing drum 1 is has a well-known structure,and is implemented as a porous cylindrical member made of stainlesssteel, and is rotatably supported on the center shaft 2 attached to apair of side plates 29L and 29R.

As shown in FIG. 3, a screen leather 50 in the strip shape is situatedacross a part of the outer surface of the printing drum 1 near a clampshaft 4s. The screen leather 50 projects approximately 1 to 2millimeters from the surface of the printing drum 1, and reinforces atrailing end of a mesh screen wrapped on the printing drum 1.

The printing drum 1 has a pair of cams 22L and 22R at its opposite sidessubstantially as integral parts, which have the same profile, and arerotatably fitted on the center shaft 2. The cams 22L and 22R are made ofplastics, and have base circles 22c and large diameter portions 22a,respectively. The large diameter portions 22a are higher than the clamp4 on the printing drum 1. The cams 22L and 22R are symmetricallysituated in such a manner that they sandwich the clamp 4 between thelarge diameter portions 22a thereof.

Referring to FIG. 3, the large diameter portions 22a of the cams 22L and22R correspond to the non-print area a of the printing drum 1 while thebase circles 22c thereof correspond to the print area b of the printingdrum 1. As shown in FIG. 4, each of the cams 22L and 22R has a pluralityof knurled dents 22b formed on each base circle 22c. These knurled dents22b are used when manually rotating the printing drum 1 so as to removea jammed stencil or printing sheet, for example. The cam disc 22L (22R)has a flange 23A (23B) on the side thereof which is in contact with aside of the printing drum 1. The flange 23A has a diameter which issubstantially as large as that of the printing drum 1. The flange 23B isbetween the base circle 22c of the cam disc 22L (22R) and the flange23A, and is somewhat larger than the base circle 22c of the cam disc 22L(22R) and the flange 23A. The flanges 23A and 23B are made of plastics,and integral with the cam disc 22L (22R). The flange 23B has a knurledperipheral edge 23a, so that the printing drum 1 can be manuallyrotated. The manual rotation of the printing drum 1 can be reliablyperformed by a well-known mechanism, not shown, including a one-wayclutch connected to a drive shaft of the ink supply roller 5 (shown inFIG. 1). The cams 22L and 22R and the flanges 23A have hollow portionsso that they are light in weight and contribute to reduce a moment ofinertia applied to the printing drum 1 during the rotation thereof. Thehollow portions of the flange 23A are not shown in FIG. 4.

As shown in FIG. 2, the press roller 9 is juxtaposed to the center shaft2 of the printing drum 1, and is a rubber roller of a well-knownstructure. The press roller 9 is substantially integral with a shaft 9s.The shaft 9s has cam followers 9L and 9R near its opposite ends outsidethe press roller 9. The cam followers 9L and 9R are in the same shape,and selectively follow the cams 22L and 22R. Each of the cam followers9L and 9R has a diameter which is smaller than that of the press roller9, so that a fine space c (shown in FIG. 3) can be maintained betweenthe printing drum 1 and the cam followers 9L and 9R. Thus, the printingsheet P is pressed to the print area b by the printing drum 1 and thepress roller 9 so as to have an image transferred thereon during theprinting process.

Referring to FIG. 2, the shaft 9s has, at its opposite ends, a pair ofbearings 9j outside the cam followers 9L and 9R. These bearings 9j arereceived by a pair of press roller arms 25L and 25R, which are in thesame shape. Each of the press roller arms 25L and 25R is movablyreceived by a support shaft 24L (24R, not shown in FIG. 2), which isconnected to a side plate 29L (29R). Each of the press roller arms 25Land 25R is vertically movable at its free end. Thus, the shaft 9s of thepress roller 9 is rotatably supported at its opposite ends by the pressroller arms 25L and 25R via the bearings 9j. Each press roller arm 25L(25R) has a step 25a at the free end thereof, which is adapted to beengaged with a pressure releasing ratchet 28L (28R) to be describedlater.

A pair of spiral tension springs 26 are situated between the centers ofthe press roller arms 25L and 25R and immovable members (which aredisposed on the side plates 29L and 29R, but not shown) above theprinting drum 1. Therefore, the press roller arms 25L and 25R arecontinuously urged upward by the spiral tension springs 26 so that thecam followers 9L and 9R are in pressure contact with the cams 22L and22R, and so that the press roller 9 is urged to rock toward the outersurface of the printing drum 1. The spiral tension springs 26 arestrictly controlled their properties such as a load, a height and aspring constant, so that the press roller 9 can come into contact withthe printing drum 1 with a uniform load during the printing process.

As shown in FIG. 5, the bearings 9j of the shaft 9s are protected bystops 27L and 27R against falling off from the press roller arms 25L and25R. Referring to FIG. 6(a), the stop 27L has a base serving as afulcrum, which is attached to the press roller arm 25L. The stop 27L issupported by a stepped screw 27a in such a manner that the stop 27L isaxially movable in a space between a click position and a non-clickposition. This mechanism facilitates loading and unloading of theprinting drum 1, and replacement and cleaning of parts such as the pressroller 9 or tension coil springs 26. FIG. 6(b) shows the stop 27R forthe press roller arm 25R.

The pressure releasing ratchets 28L and 28R selectively engage with thepress roller arms 25L and 25R so as to stop the rocking motion thereof,are near the press roller arms 25L and 25R, and are fixedly fitted on ashaft 28s which is rotatably supported on the side plates 29L and 29R.The pressure releasing ratchet 28L (28R) has a toothed portion 28a atits free end. The toothed portion 28a is adapted to selectively engagewith the step 25a of the press roller arm 25L (25R). Referring to FIG.5, a pair of tension coil springs 31 are positioned right to thepressure releasing ratchets 28L and 28R. Each of the tension spring 31is fitted on a pin 32 embedded in the side plate 29L (29R) at one endthereof, and is connected to the base of the pressure releasing ratchet28L (28R) at the other end thereof. Each of the tension coil springs 31urges the toothed portion 28a of the pressure releasing ratchet 28L(28R) to the left so that the toothed portion 28a is engaged with thestep 25a of the press roller arm 25L (25R). A pair of solenoids 33including plungers 33p are fixedly situated on the side plates 29L and29R near the pressure releasing ratchets 28L and 28R. Each of theplungers 33p is connected to the base of the pressure releasing ratchet28L (28R).

The pressure releasing ratchets 28L and 28R, shaft 28s, tension coilsprings 31 and solenoids 33 serve to hold and free the press roller 9 atand from the non-printing position.

The sheet separating pawl 15 is fastened at its base by a small screw15a on a shaft 34 which rotatably extends between the side plates 29Land 29R, and has a rectangular cross section. The sheet separating pawl15 has a free end which is selectably movable between a sheet separatingposition which is close to the outer surface of the printing drum 1 witha minimum space kept against the printing drum, and a non-sheetseparating position which is far from the printing drum 1. At the sheetseparating position, the separating pawl 15 can reliably strip a leadingedge of the printed sheet Pa off from the printing drum 1 without anycontact with the outer surface of the printing drum 1. At the non-sheetseparating position, the separating pawl 15 does not interfere with theclamp 4.

The shaft 34 includes a drive arm 36 near the side plate 29L. The drivearm 36 includes, as an integral part, a roller 35 which serves as a camfollower for the sheet separating pawl 15 (called "cam follower 35"). Atension coil spring 38 is disposed between the base of the sheetseparating arm 36 and a pin 37 embedded in the side plate 29L. Thetension spring 38 urges the drive arm 36 so that the cam 22L and the camfollower 35 are continuously in pressure contact with each other. InFIG. 2, reference numeral 39 denotes an L-shaped stop fastened at apredetermined position on the side plate 29L, and 40 denotes a screw incontact with the stop 39. Both the stop 39 and the screw 40 reliablyadjust the sheet separating pawl 15 at the sheet separating position.The screw 40 is turned so that the large diameter portion 22a of the camdisc 22L is in optimum contact with the cam follower 35 but that the camfollower 35 does not come into pressure contact with the base circle 22c(FIG. 3) and the dents 22b (FIG. 4) of the cam disc 22L. In other words,the stop 39 and the screw 40 allows the cam follower 35 to selectivelycontact only with the large diameter portion 22a of the cam disc 22L.

The operation of the foregoing stencil duplicating machine will bedescribed hereinafter. Unless otherwise specified, one each of pairedcomponents will be described.

Referring to FIG. 1, a printing sheet P is conveyed toward press roller9 via the sheet feed roller 12, separation roller pair 13a and 13b, andsheet conveying roller pair 14a and 14b. The printing sheet P reachesthe space between the printing drum 1 and the press roller 9 which arein synchronization with each other. Then, the tension springs 26 enablethe press roller 9 to be in uniform pressure contact with the printingdrum 1 via the printing sheet P and the stencil 3 wrapped round theprinting drum 1. In this state, ink oozes via the perforations of thestencil 3 and is transferred onto the surface of the printing sheet P,thereby forming an image thereon. In this state, the ink supply roller 5(shown in FIG. 3) also rotates in the same direction as that of theprinting drum 1, and supplies ink to the inner surface of the printingdrum 1. For simplification, only one of the spiral tension springs 26 isshown in FIG. 3, and the unit for holding and freeing the pressureroller 9 at and from the non-printing position are omitted therefrom.The printed sheet Pa is stripped off from the printing drum 1 by thesheet separating pawl 15, is conveyed on the conveyer belt 19 and isreceived in the discharge tray 16. Thus, the printing on one sheet iscompleted.

As shown in FIG. 5, when the printing drum 1 further rotates and thelarge diameter portion 22a of the cam 22L reaches near the press roller9, the large diameter portion 22a of the cam 22L comes into contact withthe cam follower 9L. Then, the press roller arm 25L is rocked downwardon the fulcrum 24L, so that the press roller 9 is pushed backward fromthe outer surface of the printing drum 1 against the force of thetension coil spring 26. The press roller 9 remains out of contact withthe screen leather 50 and the clamp 4. As the printing drum 1 keeps onrotating, the clamp 4 reaches near the free end of the sheet separatingpawl 15, i.e. the non-sheet separating position of the sheet separatingpawl 15. Then, the cam follower 35 (FIG. 2) comes into contact with thelarge diameter portion 22a of the cam 22L, turns counterclockwise theshaft 34 for the sheet separating pawl 15, thereby making the free endof the sheet separating pawl 15 leave away from the screen leather 50and the clamp 4. Thus, the sheet separating pawl 15 does not interferewith the screen leather 50 and the clamp 4. When the printing drum 1further rotates and the large diameter portion 22a of the cam 22L leavesfurther from the press roller 9, a succeeding sheet will be printed. Theforegoing printing process is repeated until a desired amount of printedsheets Pa is produced.

At the end of the printing process, the solenoid 33 which has beenactive is released while the press roller 9 is pressed to the printingdrum 1 via the last printing sheet P (FIG. 3). As shown in FIG. 5, thepressure releasing ratchet 28L moves to a position shown by a dashedline, and comes into contact with a flat part 25b of the step 25a of thepress roller arm 25L via a flat part 28b of the toothed portion 28athereof. When the last printed sheet Pa is discharged onto the dischargetray 16, and when the large diameter portion 22a of the cam 22L movesdownward and comes into pressure contact with the cam follower 9L, thepress roller arm 25L is rocked downward on the fulcrum 24L while theflat part 28b of the pressure releasing ratchet 28L is in contact withthe flat part 25b of the press roller arm 25L. Further, when the peak ofthe large diameter portion 22a of the cam 22L reaches near the pressroller 9, the step 25a of the press roller arm 25L and the toothedportion 28a of the pressure releasing ratchet 28L engages with eachother as shown by a dashed line. In this state, the press roller arm 25Land the pressure releasing ratchet 28L remain engaged with each othereven when the printing drum 1 makes one or more rotations. Thus, thepress roller 9 is maintained at the non-print position where it is awayfrom the printing drum 1 and the clamp 4.

In the printing operation, the solenoid 33 is actuated while theprinting drum 1 is rotating. When the peak of the large diameter portion22a of the cam 22L moves down and comes into contact with the camfollower 9L, the press roller arm 25L is slightly pushed downwardagainst the force of the tension coil spring 26. Thus, the toothedportion 28a of the pressure releasing ratchet 28L leaves from the step25a of the press roller arm 25L. Thereafter, the plunger 33P of thesolenoid 33 is withdrawn to displace the pressure releasing ratchet 28Lto the position shown by a solid line, thereby disengaging the step 25aand the toothed portion 28a of the pressure releasing ratchet 28L. Thepress roller 9 is in pressure contact with the printing drum 1 at theprinting area a thereof, and is out of contact with the printing drum 1at the non-printing area b (refer to FIG. 3).

A second embodiment of the invention will be described with reference toFIGS. 7 to 11. This embodiment is substantially similar to the firstembodiment except for the following points. In this embodiment, astencil duplicating machine is intended for duplication of images on A4size paper sheets, for example. A printing drum 1 and cams 22L and 22Rare smaller than those in the first embodiment, and an arm 136 is usedto actuate a sheet separating pawl 15 in place of the arm 36 in thefirst embodiment.

Referring to FIG. 7, the base of the arm 136 is substantially integralwith the shaft 34 at the position near the side plate 29L. The arm 136has, at its free end, rollers 35A and 35B serving as cam followers(called "cam followers 35A and 35B"). The cam follower 35A first comesinto contact with the cam 22L, selectively displacing the sheetseparating pawl 15 at the sheet separating position and the firstnon-sheet separating position. In other words, the cam follower 35Akeeps the sheet separating pawl 15 away from the screen leather 50. Thecam follower 35B comes into contact with the cam 22L after the camfollower 35A, and selectively displaces the sheet separating pawl 15from the second non-sheet separating position to the sheet separatingposition, i.e. keeps the sheet separating pawl 15 away from the stencilclamp 4 and returns the pawl 15 to the sheet separating position. Thecam followers 35A and 35B are adjacently positioned on the arm 136 sothat they come into contact with the cam 22L successively.

A tension coil spring 38 is disposed between the base of the arm 136 anda pin 37 embedded in the side plate 29L, and continuously urges the arm136 to make the cam follower 35A and/or the cam follower 35B come intocontact with the cam 22L.

In operation, the second embodiment differs from the first embodiment asdescribed below. When the printing drum 1 keeps on rotatingcounterclockwise after the completion of printing on one sheet, thelarge diameter portion 22a of the cam 22L comes down near the pressroller 9, i.e. the non-printing position, as shown in FIG. 8. In thisstate, the cam follower 9L comes into contact with the leading sectionof the large diameter portion 22a of the cam 22L, and the press rollerarm 25L is rocked downward on the fulcrum 24L. Then, the press roller 9leaves away from the outer surface of the printing drum 1 and the screenleather 50 against the force of the tension coil spring 26, so that thepress roller 9 does not interfere with the screen leather 50 and theclamp 4.

After the cam follower 9L, the cam follower 35A comes into contact withthe large diameter portion 22a of the cam 22L, thereby rocking the arm136 and turning the sheet separating pawl shaft 34 counterclockwise.Thus, the sheet separating pawl 15 stays at the first non-sheetseparating position, does not interfere with the screen leather 50.

As shown in FIG. 9, the printing drum 1 further keeps on rotating, andthe clamp 4 arrives near the sheet separating pawl 15. Then, the camfollower 35A leaves away from the large diameter portion 22a of the cam22L while the cam follower 35B comes into contact with the largediameter portion 22a of the cam 22L. Thereafter, the arm 136 rocks, andthe sheet separating pawl shaft 34 turns counterclockwise, therebypreventing the sheet separating pawl 15 from contacting with the clamp4.

when the printing drum 1 further rotates counterclockwise as shown inFIG. 10, the cam follower 35B still remains in contact with the largediameter portion 22a of the cam 22L after the clamp 4 goes away from thesheet separating pawl 15. Thus, the arm 136 rocks and the shaft 34 arein counterclockwise rotation, thereby maintaining the sheet separatingpawl 15 at the second non-sheet separating position.

Referring to FIG. 11, when the printing drum 1 further rotates, thetrailing end of the large diameter portion 22a of the cam 22L reachesnear the cam follower 35B. Then, the cam follower 35B comes out ofcontact from the large diameter portion 22a of the cam 22L. Thus, thesheet separating pawl 15 quickly returns to the sheet separatingposition.

Sequential contacting of the cam followers 35A and 35B with the cam 22Lenables the sheet separating pawl 15 to displace itself between thesheet separating position, and the first and second non-sheet separatingposition in synchronization with the rotation of the printing drum 1.

In the foregoing embodiments, a pair of cams 22L and 22R are positionedat the opposite sides of the printing drum 1 in such a manner that theirlarge diameter portions 22a sandwich the clamp 4 on the printing drum 1.Alternatively, one cam may be provided on one side of the printing drumand one cam follower may be arranged at one side of the press rollercontacting and detaching mechanism when the press roller bearings 9j arereceived in a pair of press roller arms having an integral and strongstructure.

In the second embodiment, two rollers 35A and 35B function as camfollowers, and are used to displace the sheet separating pawl 15 at thefirst and second non-sheet separating positions. Alternatively, aplurality of cam followers may be used. Further, other members which cancome into contact with the cam may be used as the cam followers 35A and35B,

What is claimed is:
 1. A stencil duplicating machine comprising:a) aprinting drum for wrapping a stencil thereon, said printing drumincluding a center shaft; b) a press roller selectively movable betweena printing position in pressure contact with the printing drum via aprinting sheet and a non-printing position away from the printing drum,said press roller including a press roller shaft; c) at least one pressroller arm for rotatably supporting opposite ends of the press roller,the press roller arm performing a rocking motion; d) a sheet separatingpawl selectively movable between a sheet separating position to strip aprinted sheet from the outer surface of the printing drum and anon-sheet separating position away from the printing drum; e) a shaftfor fixedly supporting the sheet separating pawl and moving the sheetseparating pawl between the sheet separating position and the non-sheetseparating position; f) an arm for selectively displacing the sheetseparating pawl at the sheet separating position and the non-sheetseparating position, the arm being fitted on the shaft for the sheetseparating pawl; g) at least one cam substantially integral with a sideof the printing drum, the cam being coaxially supported on the centershaft of the printing drum, having a large diameter portion at a partthereof, and selectively displacing the press roller at the printingposition and the non-printing position; h) at least one press roller camfollower for the press roller, the press roller cam follower beingfitted on the press roller shaft and following the cam; i) means forurging the press roller cam follower toward the cam; j) a sheetseparating pawl cam follower for the sheet separating pawl, the sheetseparating pawl cam follower being fitted on the sheet separating pawlarm and following the cam such that said cam actuates both said pressroller cam follower and said sheet separating pawl cam follower; and k)means for urging the sheet separating pawl cam follower toward the cam.2. A stencil duplicating machine as in claim 1, wherein a pair of camsare provided which have the same profile and are arranged in a manner tohave the same phase, and wherein a pair of press roller cam followersare provided so as to follow the pair of cams, a pair of press rollerarms are provided, and the means for urging the press roller camfollower urges the press roller arms with a uniform load.
 3. A stencilduplicating machine as in claim 1, further including means for holdingthe press roller at the non-printing position, and means for releasingthe press roller holding means from the non-printing position when thepress roller moves to the printing position for the printing operation.4. A stencil duplicating machine comprising:a) a printing drum forwrapping a stencil thereon, said printing drum including a center shaft;b) a sheet separating pawl including a tip selectively movable between asheet separating position to strip a printed sheet from the outersurface of the printing drum and first and second non-sheet separatingpositions away from the printing drum; c) a shaft for fixedly supportingthe sheet separating pawl and moving the sheet separating pawl betweenthe sheet separating position and non-sheet separating positions; d) atleast one cam coaxially supported on the center shaft of the printingdrum; e) an arm for selectively displacing the sheet separating pawl atthe sheet separating position and the first and second non-sheetseparating positions, the arm being fitted on the shaft for the sheetseparating pawl and including a first cam follower determining a timingat which the tip of said sheet separating pawl begins to move toward thefirst non-sheet separating position, and a second cam followerdetermining a timing at which the tip of said sheet separating pawlmoves to the second non-sheet separating position and a timing at whichsaid tip returns to said sheet separating position; and f) means forurging the first and second sheet separating pawl cam followers towardthe cam.
 5. A stencil duplicating machine comprising:a) a printing drumfor wrapping a stencil thereon, said printing drum including a centershaft; b) a sheet separating pawl selectively movable between a sheetseparating position to strip a printed sheet from the outer surface ofthe printing drum and a non-sheet separating position away from theprinting drum; c) a shaft for fixedly supporting the sheet separatingpawl and moving the sheet separating pawl between the sheet separatingposition and non-sheet separating position; d) at least one camcoaxially supported on the center shaft of the printing drum; e) an armfor selectively displacing the sheet separating pawl at the sheetseparating position and the non-sheet separating position, the arm beingfitted on the shaft for the sheet separating pawl and including aplurality of cam followers adapted to come into contact with the cam ona timed relation with one another; and f) means for urging the sheetseparating pawl cam followers toward the cam; the machine furtherincluding a stencil having a leading edge, and wherein the printing drumincludes a clamp for holding the leading edge of the stencil on theouter surface of the printing drum, and the plurality of cam followerscomprise a cam follower for moving a tip of the sheet separating pawlapart from the stencil and a cam follower for moving the tip of thesheet separating pawl apart from the clamp.
 6. The stencil duplicatingmachine of claim 4, wherein said second non-separating position isradially spaced from said first non-separating position with said secondnon-separating position farther from said printing drum than said firstnon-separating position.
 7. A stencil duplicating machine as in claim 2,further including means for holding the press roller at the non-printingposition, and means for releasing the press roller holding means fromthe non-printing position when the press roller moves to the printingposition for the printing operation.
 8. The stencil duplicating machineof claim 3, wherein said means for holding the press roller holds thepress roller at the non-printing position regardless of a rotationalposition of said cam of said printing drum.
 9. The stencil duplicatingmachine of claim 7, wherein said means for holding the press rollerholds the press roller at the non-printing position regardless of arotational position of said cam of said printing drum.
 10. A stencilduplicating machine comprising:a) a printing drum for wrapping a stencilthereon, said printing drum including a center shaft; b) a press rollerselectively movable between a printing position in pressure contact withthe printing drum via a printing sheet and a non-printing position awayfrom the printing drum, said press roller including a press rollershaft; c) at least one press roller arm for rotatably supportingopposite ends of the press roller, the press roller arm performing arocking motion; d) a sheet separating pawl selectively movable between asheet separating position to strip a printed sheet from the outersurface of the printing drum and a non-sheet separating position awayfrom the printing drum; e) a shaft for fixedly supporting the sheetseparating pawl and moving the sheet separating pawl between the sheetseparating position and the non-sheet separating position; f) an arm forselectively displacing the sheet separating pawl at the sheet separatingposition and the non-sheet separating position, the arm being fitted onthe shaft for the sheet separating pawl; g) at least one camsubstantially integral with a side of the printing drum, the cam beingcoaxially supported on the center shaft of the printing drum, having alarge diameter portion at a part thereof, and selectively displacing thepress roller at the printing position and the non-printing position; h)at least one cam follower for the press roller, the cam follower beingfitted on the press roller shaft and following the cam; i) means forurging the press roller cam follower toward the cam; j) a cam followerfor the sheet separating pawl, the cam follower being fitted on thesheet separating pawl arm and following the cam; k) means for urging thesheet separating pawl cam follower toward the cam; and l) an adjustingmechanism including a stop and a screw for adjusting a position of saidsheet separating pawl at said sheet separating position.
 11. A stencilduplicating machine comprising:a) a printing drum for wrapping a stencilthereon, said printing drum including a center shaft; b) a press rollerselectively movable between a printing position in pressure contact withthe printing drum via a printing sheet and a non-printing position awayfrom the printing drum, said press roller including a press rollershaft; c) at least one press roller arm for rotatably supportingopposite ends of the press roller, the press roller arm performing arocking motion; d) a sheet separating pawl selectively movable between asheet separating position to strip a printed sheet from the outersurface of the printing drum and a non-sheet separating position awayfrom the printing drum; e) a shaft for fixedly supporting the sheetseparating pawl and moving the sheet separating pawl between the sheetseparating position and the non-sheet separating position; f) an arm forselectively displacing the sheet separating pawl at the sheet separatingposition and the non-sheet separating position, the arm being fitted onthe shaft for the sheet separating pawl; g) at least one camsubstantially integral with a side of the printing drum, the cam beingcoaxially supported on the center shaft of the printing drum, having alarge diameter portion at a part thereof, and selectively displacing thepress roller at the printing position and the non-printing position; h)at least one cam follower for the press roller, the cam follower beingfitted on the press roller shaft and following the cam; i) means forurging the press roller cam follower toward the cam; j) at least firstand second cam followers disposed on said sheet separating pawl arm andfollowing the cam, wherein said first and second cam followers arespaced from one another on said sheet separating pawl arm such thatmovement of said sheet separating pawl arm is controlled by said firstcam follower during a first portion of cam rotation, and by said secondcam follower during a second portion of cam rotation; and k) means forurging the sheet separating pawl cam follower toward the cam.
 12. Thestencil duplicating machine of claim 1, further including a bearingrotatably supporting said press roller on said at least one press rollerarm, and wherein said at least one press roller arm is mounted upon ashaft and pivots about said shaft to perform said rocking motion, andwherein said at least one press roller cam follower includes a rollermember concentrically mounted upon said press roller shaft.
 13. Thestencil duplicating machine of claim 12, wherein said roller member hasa diameter smaller than a diameter of said press roller.
 14. The stencilduplicating machine of claim 5, further including a screen leatherdisposed adjacent to said clamp of said printing drum, and wherein saidcam follower for moving the tip of the sheet separating pawl apart fromthe stencil moves the tip of the sheet separating pawl apart from thescreen leather.